If you plan on backpacking extensively with your dog, there are some things you can do when they're young that will set you up to have awesome (and safe) trips, down the road.
I started both of my dogs wearing empty backpacks and going on walks around 5-6 months of age. They're taught that when the backpack is on, it's time to walk in an orderly fashion. No wrestling, no rolling in the mud, no swimming. I don't care about any sort of "heel" position, but I don't allow crazy behavior. When the backpack comes off, in camp or for a break, they can act goofy, roll, swim, wrestle with each other, etc. I did not ask my dog to carry any real weight until she was around 18-24 months old, her pack on long trips usually averages around 10lbs (she's about 70-75lbs, full adult weight). My 9 month puppy currently carries empty plastic bags, spare mittens - bulky but essentially weightless stuff.
Get in the habit of paying very close attention to your dog's eating trends, so you're 100% in tune with their body and fuel needs before you hit the trail. Hopefully your dog doesn't have any food allergies - if s/he does, this will be even more important. I'm fortunate that both of my dogs have iron stomachs and can eat most anything. Their calorie needs skyrocket on extended trips, especially in cold weather, and you'll want to plan accordingly. Kibble is pretty bulky, figure out some rich, calorie dense foods that can be added to whatever you normally feed. Tuna, butter, coconut oil, real peanut butter, lots of things work. Also, if you get stuck somewhere due to bad weather or other issues, you'll need to be able to improvise dog meals from your own stash that meet your dog's needs. It's guaranteed to happen sooner or later.... we got snowed in and stuck in the mountains in North Carolina a few days longer than expected, so I made my dog a stew of cooked un-flavored Ramen, rinsed tuna, butter, and dehydrated eggs. When every pound in your pack counts, the way I see it, I can't (or won't) eat extra kibble, but my dogs can eat extra "people" food, so that's what I pack. Don't experiment with totally new foods on a trip, the last thing you need is a barfing dehydrated dog stuck in your tent.
Expose your dog to horses, snowmobiles, mountain bikes, four-wheelers, cattle (from behind a fence), and everything else you might encounter. Some of the best backcountry trails in the USA are shared-use with equestrians, cross through active farmland and pasture, and are used legally or illegally by ATV's and cyclists. Make sure your dog knows to leave these things alone, and doesn't chase or harass any
of them. Dogs are getting banned left and right from well-known trails due to complaints from non-dog trail users, this is a serious
Teach "Leave-It", and enforce it with absolute clarity. Snakes, porcupines, other hiker's food, piles of horse droppings, dead animals, traps during hunting season, the list is endless. Teach your dog to wait at potable water sources (like springs and artisan wells) and fill a bowl for them to drink. Many hikers get justifiably furious when they get to the only potable water source within miles, only to find two muddy dogs playing in it, slobbering in it, or heaven forbid, peeing in it. This is a huge deal on long trails, and one of the biggest reasons some people want all dogs banned.
I hope some of this info is helpful, if there are any other specific things anyone wants to chat about I'm more than happy to keep rambling. I love (LOVE, LOVE, LOVE) backpacking, and I'm heading out to try a new route this weekend.